Liquid crystal devices are used in various apparatus, including middle- and large-sized apparatus such as desktop personal computers, notebook personal computers, and liquid crystal television sets as well as small mobile apparatus such as electronic organizers, mobile telephones, and digital cameras. Thin and lightweight liquid crystal panels are used in these various types of apparatus.
A liquid crystal device has a panel filled with a liquid crystal as an electro-optical conversion member. The panel is cut from a large substrate in which a plurality of panels are formed.
A technique for forming a plurality of panels in a large substrate, cutting out the individual panels, and injecting a liquid crystal into the panels will now be described with reference to FIGS. 27 and 28.
A lower large substrate 1A and an upper large substrate 2A are provided, on either one of which frame-shaped seals 7 are formed by a technique such as printing. Each frame-shaped seal 7 corresponds to one panel A plurality of frame-shaped seals 7 are arranged in a matrix on the lower large substrate 1A or upper large substrate 2A. Part of each frame-shaped seal is left open and the opening is flanked on both sides by projections 7e projecting outward to form an injection port 7f. The injection port 7f is used to inject the liquid crystal.
The seal 7 is made of a resin adhesive 7m containing gap adjustment members (referred to hereinafter as spacers) 7n for adjusting the gap between the substrates. The spacers 7n set the amount of gap (the gap dimension) between the lower and upper large substrates 1A, 2A. The resin adhesive 7m may be a thermosetting adhesive, UV-curing adhesive, or other adhesive.
Each frame-shaped seal 7 has four sides 7a, 7b, 7c, and 7d, side 7a facing side 7d and side 7b facing side 7c. The injection port 7f is located in side 7a. 
After a plurality of frame-shaped seals 7 are formed on the lower large substrate 1A or upper large substrate 2A, the lower and upper large substrates 1A, 2A are placed face to face and aligned with each other in planes parallel to the opposing surfaces of the resultant large substrate. Then, the lower and upper large substrates 1A, 2A are bonded together by heating or ultraviolet irradiation under pressure applied to the lower and upper large substrates 1A, 2A from the outside toward the inside. This bonding step forms a plurality of panels 10-1, 10-2, 10-3, . . . in the lower and upper large substrates 1A, 2A as shown in FIG. 27.
When the lower and upper large substrates 1A, 2A are bonded together, injection regions B, into which the liquid crystal is injected as the electro-optical conversion member in a subsequent step, are created inside the individual seals 7 as shown in FIG. 28.
A plurality of transparent electrodes 3 are provided for each of the panels on the surface of the lower large substrate 1A facing the upper large substrate 2A as shown in FIG. 28, and oriented films 5 are provided on the transparent electrodes 3. Similarly, a plurality of transparent electrodes 4 and oriented films 6 are provided on the surface of the upper large substrate 2A facing the lower large substrate 1A.
Each liquid crystal panel includes a liquid crystal section containing a liquid crystal sealed in the space enclosed by the frame-shaped seal and a connection electrode forming section C outside the frame-shaped seal. Connection electrodes (or wiring electrodes) disposed in the connection electrode forming section C establish electrical connections with electrodes (mainly, pixel electrodes and wiring electrodes) disposed in the liquid crystal section to transmit signals for driving the liquid crystal.
In FIGS. 27 and 28, the connection electrode forming section C of a panel occupies the space between the frame-shaped seal 7 of the panel and the frame-shaped seal 7 of the vertically adjacent panel. The connection electrode forming section C is formed on an extension C′ of the lower large substrate 1A.
As shown in FIG. 28, the connection electrode forming section C is formed only on the lower large substrate 1A. Connection electrodes 9 are disposed on the connection electrode forming section C. The connection electrodes 9 include lead wiring electrodes (or wiring electrodes) for connection to the transparent electrodes 3 in the electro-optical conversion member injection region B on the lower large substrate 1A, and for connection through a transfer-connection structure to the transparent electrodes 4 on the upper large substrate 2A.
The dot-dash lines X1, X2, X3, and Y in FIG. 27 are cleaving or cutting lines for separating the panels 10-1, 10-2, 10-3, 10-4, 10-11, . . . , 10-21, . . . from the large substrate (mother substrate) composed of the lower and upper large substrates 1A, 2A. Individual panels are obtained by cutting along these cutting lines. (An arbitrary one of the panels will be referred to hereinafter as “panel 10”.)
First, the lower and upper large substrates 1A, 2A are cut simultaneously into strips along cutting lines X3, each strip including a row of panels 10. Next, each strip is cut along cutting line X1 to remove a region K to trim the projecting tips of the projections 7e on both sides of the injection ports 7f in the seals 7. Then, the upper substrate 2A is cut along cutting line X2 as shown in FIG. 28 to remove an unnecessary portion D.
After the strips have been formed by these cuts, a liquid crystal is injected as an electro-optical conversion member into the individual panels through their injection ports 7f. Then, the injection ports 7f are sealed. Next, each strip is cut along cutting lines Y to obtain individual panels with the liquid crystal encapsulated therein, i.e., individual liquid crystal panels (liquid crystal devices).
The above manufacturing method allows a plurality of liquid crystal panels to be cut out and formed from a large substrate. A drawback has been found in this manufacturing method, however: the gap between the upper and lower substrates of each panel is not uniform over the entire panel, varying in different portions of the panel. The inventors have found a new tendency in this gap irregularity.
The plan view in FIG. 29 illustrates this problem of the above manufacturing method.
Among the sides 7a, 7b, 7c, and 7d of the frame-shaped seal 7 of a panel 10, the gap tends to be narrower in the diagonally shaded areas E1, E2 on sides 7a and 7d than in other areas.
This problem is caused by a difference in the distance between seals: the distances between side 7a of the seal of a panel 10 and side 7d of the seal of an adjacent panel 10, and between the side 7d of the seal of a panel 10 and side 7a of the seal of an adjacent panel 10 are enlarged by the connection electrode forming section C and projecting tip clipping area K between the seal members 7a, 7d of the panel 10 and the seal members 7d, 7a of the adjacent panels 10.
With reference to the large substrate in FIG. 27, the distance between sides 7a and 7d of adjacent seals is lengthened by the connection electrode forming section C and projecting tip clipping area K between side 7a of the seal in panel 10-13 and side 7d of the seal in the upper adjacent panel 10-3. Similarly, the distance between sides 7d and 7a is lengthened by the connection electrode forming section C and projecting tip clipping area K between side 7d of the seal in panel 10-13 and side 7a of the seal in the lower adjacent panel 10-23.
In comparison, side 7b of the seal in panel 10-13 is close to side 7c of the seal in the right-adjacent panel 10-14, and side 7c of the seal in panel 10-13 is also close to side 7b of the seal in the left-adjacent panel 10-14.
If the seals disposed between the lower and upper large substrates are closely spaced in some parts and more widely spaced in other parts, the more widely spaced parts of the seals tend to experience a larger thickness deformation than the closely spaced parts when external pressure is applied to bond the lower and upper large substrates together. In short, the inventors have found that the seal thickness varies in different parts of a single panel.
If such a panel, with different thickness deformations in different seal areas (causing the gap between the lower and upper large substrates to vary significantly in different panel areas), is employed in a liquid crystal display device, uneven color and other problems degrading the color image quality or display quality will appear on the display.
Although various attempts have been made to minimize the gap irregularities of large substrates, the problem found above by the inventors have not been successfully addressed in the art.
In the art described in Japanese Unexamined Patent Application Publication No. 6-75233 and illustrated in FIG. 30, for example, the distance between the centers of the lower and upper large substrates is mechanically adjusted by suction applied by a cell suctioning pump or pressure applied by a cell pressurizing compressor. FIG. 30 is a plan view showing the pattern in which the seals are disposed; each frame-shaped seal member 301 has a liquid crystal injection port 304 and is surrounded by dummy seal members 303 to balance the pressure applied to the seal material in the step of applying pressure to the substrates. No spacers are mixed into these seal members.
Japanese Unexamined Patent Application Publication No. 11-14953 discloses a technique for securing a uniform cell gap for each liquid crystal panel cut from a large substrate by surrounding each frame-shaped seal formed in the large substrate by dummy seals disposed parallel to the sides of the seal.
Japanese Unexamined Patent Application Publication No. 4-240621 discloses a technique for securing a uniform gap over the entire area of a liquid crystal panel composed of two substrates and providing a uniform thickness in the liquid crystal layer by placing the same number of spacers in the long sides of a rectangular frame-shaped seal as in the short sides.
Furthermore, a typical liquid crystal display panel has a pair of transparent substrates placed face to face, each equipped with transparent electrodes, an oriented film, and other elements, with a frame-shaped seal (encapsulating member) containing gap adjustment members (spacers) disposed in the peripheral parts between the opposite surfaces. A liquid crystal is injected as an electro-optical conversion member into the space surrounded by the seal between the opposite substrates.
A seal for a liquid crystal device will now be described with reference to FIGS. 31-35.
A liquid crystal panel 101 is composed of a lower substrate 110 and an upper substrate 120 placed face to face with a gap between them. The lower substrate 110, as shown in FIGS. 32 and 33, has a transparent substrate 111 as a base member, with transparent electrodes 112 formed by patterning on the surface of the transparent substrate 111 facing the upper substrate 120. An insulating film 113 is formed on the upper surface of the transparent electrodes 112 to prevent the transparent electrodes 112 from being short-circuited to the electrodes on the upper substrate 120 by dust or other foreign particles. The lower substrate 110 also has an oriented film 114 formed on the upper surface of the insulating film 113. When the liquid crystal panel 101 is used as a reflective liquid crystal panel, the lower substrate 110 may be opaque or semitransparent, and for an active panel TFT or MIM (TFD) elements or the like may be formed on the substrate.
The upper substrate 120 has a transparent substrate 121 as a base member, similar to the lower substrate 110, and has a color filter 122 with red (R), green (G), and blue (B) color filters arranged in a striped or matrix pattern on the surface of the transparent substrate 121 facing the lower substrate 110. As shown in FIGS. 32 and 33, a flattening film, protection film, or overcoat 123 is disposed on the lower surface of the color filter 122 to protect the color filter 122 and flatten its surface. The overcoat 123 has transparent electrodes 124 formed by patterning on its lower surface. The upper substrate 120 also has an oriented film 125 formed on the lower surface of the transparent electrodes 124.
A frame-shaped seal 130 is disposed between the lower and upper substrates 110, 120 of the liquid crystal panel 101. Spacers 131 are intermixed with the seal 130. The lower and upper substrates 110, 120 are bonded together through the seal 130.
The spacers 131 serve to maintain a uniform gap (cell gap) between the lower and upper substrates 110, 120. More specifically, the lower and upper substrates 110, 120 are positioned with a predetermined gap therebetween by the spacers 131. The region surrounded by the frame-shaped seal 130 is the space into which the liquid crystal injected. The liquid crystal 140 is injected into this space through the injection port 132 shown in FIG. 31. After a predetermined amount of liquid crystal is injected, the injection port 132 is sealed with port sealing resin 133. In this manner, the liquid crystal layer 140 shown in FIGS. 32 and 33 is formed. Intra-cell spacers 141 are scattered throughout the liquid crystal layer 140 to keep the gap (cell gap) between the substrates uniform.
A liquid crystal panel 101 having the above structure is obtained by cutting a large liquid crystal cell 501, shown as a large substrate (mother substrate) in FIG. 34, on which a plurality of liquid crystal panels are created at once, then injecting a liquid crystal into each liquid crystal cell, and sealing each injection port. The upper and lower substrates constituting the large liquid crystal cell 501 are first cut simultaneously along the cutting lines marked X-X1. Then, the upper substrate is cut along cutting lines X2-X3 to obtain strips each including a plurality of liquid crystal cells arranged in a row.
A liquid crystal is injected through the respective injection ports of the individual liquid crystal cells in the strips; then the injection ports are sealed, and the upper and lower substrates including the liquid crystal cells are cut simultaneously along cutting lines Y-Y1 in FIG. 34 to produce individual liquid crystal panels.
The large liquid crystal cell 501 shown as the mother substrate in FIG. 34 is formed by overlaying the upper large substrate 520 shown in FIG. 35(B) face to face on the lower large substrate 510 shown in FIG. 35(A). Seals 130 arranged as a plurality of rectangular frames are formed on the lower large substrate 510. No seals 130 are formed on the upper large substrate 52.
The transparent electrodes 112, insulating films 113, and oriented films 114 shown in FIGS. 32 and 33 (not shown in FIG. 35(A)) are disposed on the surface 510F of the lower large substrate 510 facing the upper large substrate 520 in FIG. 35(A). A plurality of frame-shaped seals 130 are also disposed as described above on the lower large substrate 510.
The color filters 122, overcoats 123, transparent electrodes 124, and oriented films 125 shown in FIGS. 32 and 33 (not shown in FIG. 35(B)) are disposed on the surface 520F of the upper large substrate 520 facing the lower large substrate 510 in FIG. 35(B).
A liquid crystal panel 101 produced from this large liquid crystal cell 501 has the following problems.
As shown in FIG. 31, an extension 110A of the lower substrate 110 protrudes beyond the associated end of the upper substrate 120. The side 130A of the seal adjacent to the extension 110A of the lower substrate 110 and the opposite side 130A (provided with the injection port 132) contain spacers 131 having a particle size of approximately 6.0 μm. Accordingly, the thickness of these sides 130A of the seal, corresponding to the gap between the opposite substrates, is on the average approximately 6 μm, this gap being defined by the particle size of the spacers 131.
The sides 130B of the seal that meet sides 130A at right angles contain spacers of the same size and material as those above, so the thickness of these sides 130B, corresponding to the gap between the opposite substrates, is also approximately 6 μm, defined by the particle size of the spacers 131.
The inventors have found that the luminance observed near sides 130A of the seal is different from the luminance observed near sides 130B when the completed liquid crystal panel is illuminated by a backlight. Through investigation, the inventors have found that this problem is caused by a difference in flattening between the spacers 131 in sides 130A and the spacers 131 in the sides 130B perpendicular to sides 130A. This will be described below with reference to the cross-sectional views of a representative side 130A in FIG. 32 and a representative side 130B in FIG. 33.
FIGS. 32 and 33 show the degrees of flattening of the spacers 131 in the sides 130A and 130B of the seals. The flattening of the spacers 131 in the side 130A of the seal shown (with some exaggeration) in FIG. 32, is significantly greater than the flattening of the spacers 131 in the side 130B of the seal shown in FIG. 33. More specifically, the spacers 131 in FIG. 32 are flattened enough to reduce the gap between the opposite substrates to approximately 5.5 μm, while the spacers 131 in FIG. 33 are flattened less and the gap between the opposite substrates remains approximately 6.0 μm.
It has been found that this gap difference of approximately 0.5 μm between sides 130A and 130B of the seal, which are disposed in different locations in the panel, causes luminance unevenness M in the peripheral parts around the display area Z (the effective panel area) of the liquid crystal panel 101 shown in FIG. 31 and thereby degrades the display quality.
Accordingly, the inventors examined how the positional difference of the sides of the seal causes such luminance unevenness near the seal in the panel.
Through investigation of the gap between the upper and lower substrates of a liquid crystal panel 101 obtained from a large liquid crystal cell 501 as shown in FIG. 34, it has been found that the gap S2 (FIG. 32) appears in areas corresponding to sides 130A of the seals in FIG. 35(A) and the gap S3 (FIG. 33) appears in areas corresponding to sides 130B of the seals in FIG. 35(A).
This is because in the large liquid crystal cell 501, mutually adjacent sides 130A of the seals are relatively distant from each other because of the extension 110A interposed between them, while mutually adjacent sides 130B of the seals are relatively close together because there is no extension 110A between them.
More specifically, the narrowly spaced sides 130B of the seals (spaced close together) are thought to be more resistant to the external pressure applied when the large liquid crystal cell 501 is manufactured and to be able prevent the spacers 131 in the seal from being significantly flattened. In contrast, the more widely spaced sides 130A of the seals are thought to be less resistant to the pressure applied when the large liquid crystal cell 501 is manufactured; the individual spacers 131 in sides 130A of the seals are subject to more pressure and suffer more flattening.
A difference is accordingly inferred to occur between the gaps S2 and S3 between the upper and lower substrates at sides 130A and 130B of the seal (after the seal is deformed).